Champion D21 Sparkpulgs defective?

[Denny Clayton]

I bet those Champion D-21's will work fine, now.

[SundaySailor]

I bet those Champion D-21's will work fine, now.

Denny, some of them may be good, but I've already tested a couple and since they were soaked with gas for so long a period of time, I couldn't get them to fire using either of the other known firing cylinders.

My plan is to throw all of those plugs away so I will not get them mixed up. Plus, I need all the extra space in my tool box that I can get.

Good thought though.

I'm planning on getting four hotter plugs than the Autolite 386's. With garden time around the corner, I want all the power I can get.

Cheers!

[Mr E]

Replaced coil with brand new Bosch 12V high energy coil. (My tractor was converted to 12 vdc). No change.

Kept scratching my head. At one time with new plugs, it was firing on all four cylinders. That meant the wires had to be somewhat good.

Pulled distributor cap and rotor. The center pole for the coil wire was sheared on about 1/2 of that pole, causing the rotor to hit & miss depending on the weather conditions.

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Hope you can see the photos well enough. Replaced rotor button and distributor cap, and she's purring like a well tuned sewing machine.

Now that I see the photos, I can see a hairline crack too. That would also explain why it stumbled more when it was very humid here as opposed to when it was dry.

Garden Time!!!!


Thanks folks for the ideas. I'm up and running as far as I'm concerned.

So what do you figure happened to the cap?

[Eugene]

I'm planning on getting four hotter plugs than the Autolite 386's. With garden time around the corner, I want all the power I can get.

Hotter plugs will not provide more power from the engine. If you want a hotter spark, open up the gap a bit.

Hotter plugs will fire through some fouling. Just looked the spark plugs pictured, I didn't see any fouling.

[SundaySailor]

"So what do you figure happened to the cap?"

Don't have a clue about what happened to the cap. Wear I can understand, but the crack in it has me baffled. I'm surprised I caught it with my vision being as bad as it is. Bifocals aren't exactly the best thing since sliced bread - no matter what the doctor may tell you.

"Hotter plugs will not provide more power from the engine. If you want a hotter spark, open up the gap a bit.

Hotter plugs will fire through some fouling. Just looked the spark plugs pictured, I didn't see any fouling."

New plugs are gapped at .021. Think I'll leave them there and live with it. Just called auto parts store, and they said they didn't really have a much hotter plug than the Autolite 386. Go figure.

I think I'll keep an extra set of pre-gapped plugs in the tool box (protected) just in case of a field failure again. Might even consider a spare distributor cap and rotor button once things calm down some.

[Rick Spivey]

.021" sounds too tight, but I'm in France with limited access to stuff on the web. Older engines used to run at .035" on spark plug gap. Somebody help me here, what is correct spark gap for the Cub?

[Eugene]

.023" per the 1967 Operator's Manual.

Same gap in the 1973, 154 Operator's Manual

[SundaySailor]

.023" per the 1967 Operator's Manual.

Thanks Eugene. I had looked it up with the search function here and found multiple references to .021. Will pull the plugs and reset to .023.

Every little bit counts!

[Scrivet]

Operator's Manual says .023"

[Smokeycub]

Now that I see the photos, I can see a hairline crack too.

Not that it matters but I think that is a carbon track. A path the spark will follow at the wrong time, causing a misfire. Probably a result of the bad coil terminal in the cap. They can also occur when a wire or plug is bad.

[SundaySailor]

Now that I see the photos, I can see a hairline crack too.

Not that it matters but I think that is a carbon track. A path the spark will follow at the wrong time, causing a misfire. Probably a result of the bad coil terminal in the cap. They can also occur when a wire or plug is bad.

I'll check that again, but I'm pretty sure it's a crack. I remember going back to the distributor cap with a bright flashlight - Maglite with LED. It showed up very well then. Also, when I ran a finger nail across it, my finger nail caught on the crack.

Good to know a carbon track could cause arcing like that though.